One of conventional optical switching devices are described in the U.S. Pat. No. 4,322,126 patented on Mar. 30, 1982. The optical switching device is connected to a plurality of input optical fibers through which input light signals are supplied thereto and a plurality of output optical fibers through which switched light signals are supplied therefrom to a next stage in an optical transmission system. Between the input and output optical fibers, there is provided a light signal switching medium of , for instance, glass plate for converting each of the input light signals into parallel light beams.
In operation, the glass plate slides vertically to light paths in accordance with the electromagnetic force induced by a driver coil so that the glass plate is positioned on the light paths in the first controlled state, and moved away therefrom in the second controlled state. In the above shift of the glass plate, the light paths are changed-over between the input and output optical fibers.
A further conventional optical switching device is described in Japanese Utility Model laid-open No. 53-158247 laid open on Dec. 12, 1978. The optical switching device comprises a glass plate provided between one input optical fiber and a plurality of output optical fibers. The glass plate has light input and output surfaces parallel to each other wherein the light output surface is of a stair-like configuration for providing a plurality of light output planes, while the light input surface is of a single light input plane.
In operation, the glass plate is inserted between the input optical fiber and the plurality of output optical fibers in a posture that the light input plane and the light output planes are on the slant in regard to light paths. In this situation, an input light signal supplied from the input optical fiber is incident to the light input plane of the glass late, and then radiated from one of the light output planes which corresponds to one of the output optical fibers. As a result, the corresponding optical fiber is optically connected through the glass plate to the input optical fiber so that a light path is changed-over.
A still further conventional optical switching device is described in Japanese Patent laid-open No. 53-135650 laid open on Nov. 27, 1978. The optical switching device comprises at least one input optical fiber held in a first rotary holder and a plurality of output optical fibers held in a second rotary holder. The first and second rotary holders are in contact on respective flat planes with each other and rotated on a common axis.
In operation, the input optical fiber is optically connected to an output optical fiber selected from the plurality of output optical fibers in accordance with a relative rotation of the first and second holders. As a result, a light signal supplied from the input optical fiber is switched to the selected output optical fiber.
According to the first and second conventional optical switching devices, however, there are disadvantages that a stable motion of the glass plate is not maintained for a long time because a sliding friction of a mount supporting for the glass plate thereon is largely varied in a sliding groove depending upon the surface condition of the sliding groove, and that the stopped position of the glass plate is minutely varied in the aforementioned first controlled state thereby resulting in the fluctuation of the insertion loss and the deterioration of the reproducibility in changing-over the light paths because the formation of a gap is inevitable between the mount and the sliding groove.
According to the third conventional optical switching device, however, there is a disadvantage that it becomes large and complicated in its construction because a ball and roller bearing must be adopted in a practical use.